Prostaglandins (PGs), cyclooxygenase (COX) derived metabolites of arachidonic acid, mediate an array of physiologic functions including inflammation and oxidative stress. Epidemiological studies demonstrate that prolonged use of Non-Steroidal Anti-inflammatory Drugs (NSAIDs), which inhibit COX action, reduce the incidence of Alzheimer?s Disease (AD). Paradoxically, administration of NSAIDs in older populations increased A?42 accumulation and dementia risk. The driving force of this proposal is to reconcile these findings. The physiological effects of the COX metabolite PGE2 are mediated by four receptors, designated the E-Prostanoid (EP) receptors EP1 to EP4. EP receptors, primarily via EP3, mediate the pro-inflammatory response through the generation of reactive oxygen species (ROS), highly reactive levuglandins, and the activation of the immune-inflammatory response. Alzheimer?s disease (AD), is associated with increases in oxidative stress, and mice with an EP3 receptor knockout display a decrease in several markers of ROS generation. The EP3 receptor is unique among the prostaglandin receptors in that multiple splice variants exist. In mouse, three variants ?, ?, and ? have identical ligand binding properties, but differ in aspects of signal transduction. One of the most relevant differences among splice variants is the relative constitutive, agonist independent activity. Our hypothesis is that expression of the constitutively active splice variant of EP3, EP3?, increases with age. EP3? signals in the absence of PGE2 ligand and thus is insensitive to the action of NSAIDs. The hypothesis to be tested in this application is that EP3 receptors regulate inflammation and ROS generation, accelerating AD in an increasingly ligand independent manner. We further hypothesize that in aging individuals, a shift to constitutively active EP3? renders NSAID inhibition of PG production ineffective and possibly detrimental. To test our hypothesis, we propose the following specific Aims: Specific Aim 1. To determine changes in EP3 receptor splice variant expression in the brain over time. We will assess expression in the brains of APPSwe-PS1DE9 mice on the C57BL/6 background and WT controls. We hypothesize that EP3? expression will increase over time and predominate in older mice. We expect that inflammatory markers will increase in parallel with EP3? expression and become refractory to NSAID treatment. To test this hypothesis in Specific Aim 2. We will assay inflammatory markers and correlate this with EP receptor expression levels and NSAID treatment. We hypothesize that the increase in inflammatory markers will be blunted by NSAID treatment in mature-adult but not old mice. Proposed studies will assess whether EP3? expression is increased with aging and whether EP3 activity can be targeted in treatment and/or prevention of AD.